Improper gene expression (see Project I) could result from epigenetic and/or mutational-like changes in the genetic apparatus of cells. This project is designed to determine if such physico-chemical alterations of chromatin occur that could account for the altered gene expression previously found. General physico-chemical properties of chromatin from liver and brain of mouse appears to change with age in terms of a decrease in extractability of chromosomal proteins and a decrease in T3-hormone binding capacity to chromatin and to intact nuclei. Specific gene changes are also indicated by a decrease in availability of ribosomal genes to DNA.RNA hybridization using ribosomal RNA.